The present invention relates to components and assemblies useful in microelectronic assemblies, to assemblies incorporating such components and to methods of making such components.
Microelectronic elements such as semiconductor chips typically are provided in packages which protect the semiconductor chip itself from the external environment and which facilitate mounting the chip on a circuit board. For example, some microelectronic packages include a connection component incorporating a dielectric element such as a board or sheet having top and bottom surfaces and having electrically conductive terminals exposed at the bottom surface. The chip is mounted to the top surface and connected to the terminals by various arrangements such as electrically conductive traces extending on a surface of the dielectric element, or within the dielectric element. The chip typically has a front surface with small contacts thereon and an oppositely-facing rear surface. The chip may be mounted in a face-down arrangement, so that the front surface of the chip confronts the top surface of the dielectric element and the rear surface of the chip faces upwardly, away from the dielectric element. In other cases, the chip may be mounted in a face-up arrangement, with the rear surface of the chip facing downwardly toward the top surface of the dielectric element. The contacts on the front face of the chip typically are connected to the traces on the dielectric element either by direct bonds between the contacts and leads formed integrally with the traces, or by wire bonds. As disclosed, for example, in U.S. Pat. No. 6,177,636, the disclosure of which is incorporated by reference herein, similar chip packages can be made with terminals in the form of posts projecting from the bottom surface of the dielectric element. The posts can be fabricated using an etching process. As disclosed in commonly assigned, co-pending U.S. Provisional Patent Applications 60/533,210; 60/533,393; and 60/533,437, all filed Dec. 30, 2003, the disclosures of which are incorporated by reference herein, packages utilizing posts can provide numerous advantageous features. For example, the posts and the dielectric layer or layers can be configured to promote tilting of the posts when the tips of the posts are engaged with a test socket, to facilitate effected contact between the tips of the posts and the contacts of the test socket.
Efforts have been made to fabricate electronic connection structures such as individual layers for multi-layer circuit boards using a metallic post structure. In one process, disclosed by the North Corporation of Tokyo, Japan, a metallic plate is etched to form numerous metallic posts projecting from the plate. A dielectric layer is applied to this plate so that the posts project through the dielectric layer. An inner or upper side of the dielectric layer faces upwardly toward the metallic plate, whereas the outer or lower side of the dielectric layer faces downwardly towards the tip of the posts. The dielectric layer may be fabricated by coating a dielectric such as polyimide onto the plate around the posts or, more typically, by forcibly engaging the posts with the dielectric sheet so that the posts penetrate through the sheet. Once the sheet is in place, the metallic plate is etched to form individual traces on the inner side of the dielectric layer extending to the bases of the various posts.
The components made by this process suffer from certain drawbacks for use as connection components in certain types of semiconductor chip packages. For example, it is often desirable to mount a chip in a face-down orientation and connect the contacts on the chip to the traces of the connection component using wire bonds which extend from the chip through a large opening or slot in the dielectric element, or around the edges of the dielectric element, and approach the outer or bottom surface of the dielectric element. Such a wire bond can be formed in a simple, one-step bonding operation. However, in the aforementioned process, the traces are formed on the inner or upper side of the dielectric element. Therefore, the traces are not exposed for making such a simple, one-step wire bond connection to the contacts on the chip.
One solution to this problem is to use a two-step wire-bonding procedure, in which the bonding wires are connected to the traces before the chip is placed on the component, leaving free ends of the wires projecting across the slot or beyond the edges of the dielectric element. After placing the chip on the connection component, the free ends of the wires remain accessible so that the free ends of the wires can be bonded to the contacts of the chip in a second bonding step. The two-step bonding process, however, adds to the cost and complexity of the assembly procedure, and creates the risk of defects such as adhesive contamination of the chip contacts or bonding wires during the chip mounting step and misalignment of the free ends of the bonding wires with the chip contacts.
As disclosed in certain embodiments of co-pending, commonly assigned U.S. Provisional Patent Application 60/508,970, filed Oct. 6, 2003, the disclosure of which is hereby incorporated by reference herein, a connection component including posts can be provided with pads exposed at the bottom or outer surface of the dielectric. The component can be fabricated by uniting a metallic sheet having posts thereon with a dielectric layer as discussed above, so that the metallic sheet is disposed on the top or inner surface of the dielectric layer and the posts project through the dielectric layer and project beyond the bottom surface of the dielectric layer. Some of the posts are crushed, abraded or otherwise treated so as to convert these posts to pads which project only slightly from the outer or bottom surface of the dielectric. The metallic sheet is etched to form traces which connect the pads to the posts. The pads may be formed adjacent edges of the dielectric, or adjacent slots in the dielectric. Such a component may be assembled with a chip in face-down orientation, with the contacts of the chip disposed outside of the edges of the dielectric or in alignment with the slots in the dielectric. The pads, and hence the traces and posts, can be connected to the contacts on the chip by a simple, one-step wire-bonding procedure.